Further Analysis on the Mystery of the Surveyor III Dust Deposits l l 3 Philip Metzger , Paul Hintze , Steven Trigwele, John Lane 1 Granular Mechanic and Regolith Operations Lab, NASA, Kennedy Space Center, FL 32899 2 Applied Technology, Siera Lobo-ESC, Kennedy Space Center, FL 32899 3 Granular Mechanics and Regolith Operations, Easi-ESC, Kennedy Space Center, FL 32899 ABSTRACT The Apollo 12 lunar module (LM) landing near the Surveyor 1lI spacecraft at the end of 1969 has remained the primary experimental verification of the predicted physics of plume ejecta effects from a rocket engine interacting with the surface of the moon. This was made possible by the return of the Surveyor 1lI camera housing by the Apollo 12 astronauts, allowing detailed analysis of the composition of dust deposited by the Apollo 12 LM plume. It was soon realized after the initial analysis of the camera housing that the LM plume tended to remove more dust than it had deposited. In the present study, coupons from the camera housing were reexamined by a KSC research team using SEMIEDS and XPS analysis. In addition, plume effects recorded in landing videos from each Apollo mission have been studied for possible clues. Several likely scenarios are proposed to explain the Surveyor III dust observations. These include electrostatic attraction of the dust to the surface of the Surveyor as a result of electrostatic charging of the jet gas exiting the engine nozzle during descent; dust blown by the Apollo 12 LM fly-by while on its descent trajectory; dust ejected from the lunar surface due to gas forced into the soil by the Surveyor 1lI rocket nozzle, based on Darcy's law; and mechanical movement of dust during the Surveyor landing. Even though an absolute answer is not possible based on available data and theory, various computational models are employed to estimate the feasibility of each of these proposed mechanisms. Scenarios are then discussed which combine multiple mechanisms to produce results consistent with observations. BACKGROUND In 1967, an unmanned robotic landing device known as Surveyor III, lifted off from thefor Earth on April 17 and landed on the moon on April 20. The location ofthe Surveyor III landing was at the Mare Cognitum portion of the Oceanus Procellarum (30 01' 41.43S" 23° 27' 29.55"W). Surveyor III transmitted 6,315 photographic images back to the Earth. The landing of the Surveyor III was far from smooth. According to Wikipedia: As Surveyor III was landing (in a crater, as it turned out), highly reflective rocks confused the spacecraft's lunar descent radar. The engines failed to cut offat 14 feet (4.3 meters) in altitude as calledfor in the mission plans, and this delay caused the lander to bounce on the lunar surface twice. Its first bounce reached the altitude of about 35 feet (10 meters). The second bounce reached a height ofabout 11 feet (three meters). On the third impact with the surface - from the initial altitude ofthree meters, and velocity ofzero, which was be/ow the planned altitude of 14 feet (4.3 meters), and very Figure 1: Astronaut Bean examining slowly descending -Surveyor III settled down to a soft Surveyor III. Note that the Apollo 12 LM landing as intended. is in the background. 1 For over 2 years, Surveyor III simply resided on the surface being exposed to the ravages of space. However, on November 14, 1969, Apollo 12 launched from the Earth (despite being struck twice by lightning during take-off) and landed on the moon on November 19, 1969 at Oceanus ProcellarumlMare Cognitium (Ocean of StormslKnown Sea) at coordinates 3°00'45"S 23°25'18"W or 3.012389°S 23.421569°W. The Lunar Module (LM) of the Apollo 12 named Intrepid purposely landed 155 m to the west from Surveyor III. Apollo 12 astronauts Charles "Pete" Conrad (Commander) and Alan L. Bean (LM Pilot) were able to examine Surveyor III (as shown in Figure 2) and bring parts back to the Earth. It is interesting to note that the seismometers the astronauts had left on the lunar surface registered the vibrations from the LM lift-off for more than an hour. The relative landing sites of the Apollo 12 LM and Surveyor III are shown in Figure 2. The astronauts visited the Surveyor IlIon their second excursion. Lunar samples were taken throughout the excursions totaling a combined weight of 34 kg of rocks, soil, and core samples (taken down to 40 em below the surface regolith). A chemical analysis of most of the samples can be found on the Lunar and Planetary Institute website (http://www.lpi.usra.edu/lunar/missi ons/apollo/apollo_12/samples). Figure 2: Landing sites of Intrepid and Surveyor III. Samples taken near the LM and others taken near to Surveyor III have been tabulated in Appendix A. The goal is to observe if the elemental analysis from XPS and SEMlEDX done in the present study correlates with soil/rocks either near the LM site or near the Surveyor III site. LU AR SURVEYOR III SAMPLES The Surveyor III parts brought back to Earth by Apollo 12 are currently stored at the Johnson Space Center (JSC) Lunar Sample Curation (http://www-curator.jsc.nasa.gov/lunar /index.cfrn), and information on the chemical analyses is found at the Lunar and Planetary Institute (http://www.lpi.usra.edu). Several of the parts were requested and sent to KSC for analysis in the present study (see and Figures 3 and 4). Those parts are summarized in Table 1. 2 I~ 11 Figure 3: The camera module showing the bottom cutout. I Figure 4: Surveyor III camera on the mOOD. Table 1. Surveyor III Parts Under Investigation. Type ofSample Part Designation Comments Sample from the camera JPL#1037 bottom. JPL #2048 Flat side ofcamera. Sample from camera pointing JPL #2049 Cutouts from the Surveyor away from the Apollo 12 LM. Sample from camera pointing III Camera JPL #2050 (JSC #3160026) towards the Apollo 12 LM. Sample from camera pointing JPL #2051 (JSC #3160027) towards the Apollo 12 LM. Sample from camera pointing JPL #2052 away from the Apollo 12 LM. Acetate Tape Samples of 327082 052 the Regolith Material (collected from underneath 327 083 053 the camera clamp) Section of Cylindrical Rod Sample from each end (strut for the radar) PARTICLE MODELING AND SIMULATION Shear Stress Simulations ofLM Engine Plume Flyby Starting with a Fluent CFD simulation of the Apollo LM engine in a lunar-like environment (background pressure is artificially set to a small non-zero value in order to achieve 3 convergence), three gas parameters are computed for every point in a 2D non-uniform spatial grid: gas density fi...k), gas temperature T(k), and gas velocity v(k). Each CFD simulation and computed gas parameter output set corresponds to a specific engine height h above the lunar surface. The CFD simulation generates gas parameter data at specific spatial points corresponding to the x-y coordinates contained in the grid point array, r(k). Note that for the Fluent CFD cases considered in this report, vertical positions are described by the coordinate x and horizontal positions are described by the coordinate y. Since the CFD generation of spatial points is based on algorithms which are used to minimize error in partial differential equations describing the laws of fluid mechanics, the grid points for all practical purposes are randomly distributed. Therefore, finding a specific point nearest a field point x-y and its nearest neighbors, involves searching'the entire r(k) array for k = 1... N. To compute the shear stress from the CFD output, the grid data is resampled along the lunar surface boundary at rmn = (mtu, n~y) for m = 0, 1, 2 and n = 0... Nx . The shear stress is defined by: av T == /l ---.1::.ax (1) where fl is the dynamic viscosity of the gas, vy is the horizontal component of the gas velocity along the horizontal surface boundary, and x is the distance above the surface. The gas dynamic viscosity is a function of temperature and can be computed by Sutherland's formula approximation: ~ + C (T)3/2 (2) /l(T) == /lo ; + C To where the parameters flo, C, and To are dependent on the gas composition. A discrete approximation to the shear stress of Equation (1) can be computed usmg the resampled CFD output: vY2n -vYOn T ==Iln' , (3) n 2L1x where _ To + C (T1,n)3/2 (4) /In /lo T C ~ = 1,n + 0 An equivalent shear velocity (sometimes referred to as saltation velocity) can be computed from Equation (3) and the resampled gas density: 1/2 Tn (5) Un= ­ () P1,n SIMULATION RESULTS Shear stress along the surface has been computed for the five cases generated by Fluent CFD: h = 5, 10, and 20 [ft] and h = 25 and 45[m). The shear stress is computed and plotted for these 4 .-------------------~----------------------------------- five cases in Figure 16. The shear stress in this figure was generated with & = 0.001 [m] in Equation (3). Shear Stress Using Sutherland's Formula for Dynamic Viscosity 100 10 co !h <-- CFD Domian End ---> If) If) ~ :;; Q> -'= (f) 0.1 - Cl (h =20ft) - C7(h= 10ft) 0.01 - C2(h =5ft) - LM Fly-by (h = 25 m) - LM Fly-by (h = 45 m) 0.001 0 2 4 6 8 10 12 14 Distance from Nozzle [m) Figure 5: Shear stress along the x = Ax surface for five cases generated by Fluent CFD: h = 5, 10, 20, 25, and 451ft). Threshold Shear Stress Velocity Starting with the approach ofSagan (1990), the threshold shear stress velocity is: (5) where, (6) and, A.